vibration/grind upon takeoff

I recently noticed that upon a quick takeoff, I can hear and feel a bit of a vibration. It's kind of like a squeaky hum. (kinda tickles the nads a bit ;D) At first I thought it was my rear brake catching, so I did it a couple more times. It happens just as the clutch is disengaging. I'm not excessivley clutching upon the launch, I was getting clean takeoffs. I was wondering if anyone has experienced this before...